Fabrication of high-aspect-ratio fused silica microstructures with large depths using Bessel-beam femtosecond laser-assisted etching

We propose a facile method for the fabrication of high-aspect-ratio (HAR) fused silica microstructures with large depths using Bessel-beam femtosecond laser direct writing followed by selective chemical etching. First, laser-modified micropatterns with tunable aspect ratios are created in glass using backside Bessel laser irradiation. Then, surface and embedded glass microstructures are formed by selective removal of laser-modified regions through chemical etching. To demonstrate the capability of the proposed method, a vertical surface trench with an aspect ratio of ∼98, a depth of 2.82 mm, and a tapered angle of only ∼0.16°, and a series of periodic column array structures with 3D tunable feature sizes have been processed. Moreover, 3D multi-layer fabrication of embedded microchannels with HAR features has been demonstrated. Compared with conventional Gaussian-beam laser pulses, the proposed Bessel-beam method exhibits superior performance for ultrafast laser manufacturing of HAR glass microstructures with large depths.